Satellite networks have played an increasing important role in modern communication system for their flexible and
convenient feature. It is obvious that satellite communication systems tend to be hybrid networks and IP networks in the
future. They will provide data broadcasting services and Internet services. As in all other networks, security is a severe
challenge in satellite systems. In this paper, we construct a three-layer hierarchical satellite system and propose a
protocol for it. The protocol includes inter-layer security and end-to-end security. We apply asymmetric cryptography
and symmetric cryptography to provide security and efficiency as well. This protocol is also suggested to protect the
satellite network from eavesdropping, sophistication, masquerade and repudiation.